In particular, the senators call out a 2007 statement from Google executive Marissa Mayer that Google sometimes favored its own properties in some kinds of search results.

When the Senate asked Schmidt if that was accurate, he admitted it was in his written testimony -- although only for so-called OneBox results (those are specially formatted search results that show up at the top of some queries -- like movie listings when you search on a movie title).

But that admission was enough to set the senators on the warpath: "...this is a clear admission of Google preferencing Google results. As consumer surveys show that 88 percent of consumers click on one of the first three links, these statements appear significant when analyzing Google's potentially anti-competitive practices."

The senators also expressed concern that Google has 97% market share on mobile searches, and that competitors like Yelp and Nextag say they wouldn't launch today because of how Google's search practices have changed.

That said, the U.S. government has not brought any antitrust charges against Google yet, and the senators were careful to take "no position on the ultimate legality of Google's practices."